Neisseria meningitidis (meningococcus) is a Gram negative bacterium frequently isolated from the human upper respiratory tract. It is a cause of serious invasive bacterial diseases such as bacteremia and meningitis. The incidence of meningococcal disease shows geographical, seasonal and annual differences (Schwartz, B., Moore, P. S., Broome, C. V.; Clin. Microbiol. Rev. 2 (Supplement), S18-S24, 1989). The bacterium is commonly classified according to the serogroup if its capsular polysaccharide.
Most disease in temperate countries is due to strains of serogroup B and varies in incidence from 1-10/100,000/year total population—sometimes reaching higher values (Kaczmarski, E. B. (1997), Commun. Dis. Rep. Rev. 7: R55-9, 1995; Scholten, R. J. P. M., Bijlmer, H. A., Poolman, J. T. et al. Clin. Infect. Dis. 16: 237-246, 1993; Cruz, C., Pavez, G., Aguilar, E., et al. Epidemiol. Infect. 105: 119-126, 1990).
Epidemics dominated by serogroup A meningococci, mostly in central Africa, sometimes reach incidence levels of up to 1000/100,000/year (Schwartz, B., Moore, P. S., Broome, C. V. Clin. Microbiol. Rev. 2 (Supplement), S18-S24, 1989). Nearly all cases as a whole of meningococcal disease are caused by serogroup A, B, C, W-135 and Y meningococci, and a tetravalent A, C, W-135, Y capsular polysaccharide vaccine is available (Armand, J., Arminjon, F., Mynard, M. C., Lafaix, C., J. Biol. Stand. 10: 335-339, 1982).
The frequency of Neisseria meningitidis infections has risen in the past few decades in many European countries. This has been attributed to increased transmission due to an increase in social activities (for instance swimming pools, theatres, etc.). It is no longer uncommon to isolate Neisseria meningitidis strains that are less sensitive or resistant to some of the standard antibiotics. This phenomenon has created an unmet medical need and demand for new anti-microbial agents, vaccines, drug screening methods, and diagnostic tests for this organism.
The available polysaccharide vaccines are currently being improved by way of chemically conjugating them to carrier proteins (Lieberman, J. M., Chiu, S. S., Wong, V. K., et al. JAMA 275: 1499-1503, 1996).
A serogroup B vaccine, however, is not available. The serogroup B capsular polysaccharide has been found to be nonimmunogenic—most likely because it shares structural similarity with host components (Wyle, F. A., Artenstein, M. S., Brandt, M. L. et al. J. Infect. Dis. 126: 514-522, 1972; Finne, J. M., Leinonen, M., Mäkelä, P. M. Lancet ii.: 355-357, 1983). Effort has therefore been focused in trying to develop serogroup B vaccines from outer membrane vesicles (or blebs) or purified protein components therefrom.
Alternative meningococcal antigens for vaccine development are meningococcal lipooligosaccharides (LOS). These are outer membrane bound glycolipids which differ from the lipopolysaccharides (LPS) of the Enterobacteriaceae by lacking the O side chains, and thus resemble the rough form of LPS (Griffiss et al. Rev Infect Dis 1988; 10: S287-295). Heterogeneity within the oligosaccharide moiety of the LOS generates structural and antigenic diversity among different meningococcal strains (Griffiss et al. Inf. Immun 1987; 55: 1792-1800). This has been used to subdivide the strains into 12 immunotypes (Scholtan et al. J Med Microbiol 1994, 41:236-243) Immunotypes L3, L7, & L9 are immunologically identical and are structurally similar (or even the same) and have therefore been designated L3,7,9 (or, for the purposes of this specification, generically as “L3”). Meningococcal LOS L3,7,9 (L3), L2 and L5 can be modified by sialylation, or by the addition of cytidine 5′-monophosphate-N-acetylneuraminic acid. Although L2, L4 and L6 LOS are distinguishable immunologically, they are structurally similar and where L2 is mentioned herein, either L4 or L6 may be optionally substituted within the scope of the invention. Antibodies to LOS have been shown to protect in experimental rats against infection and to contribute to the bactericidal activity in children infected with N. meningitidis (Griffiss et al J Infect Dis 1984; 150: 71-79).
A problem associated with the use of LOS in a meningococcal vaccine, however, is its toxicity (due to its Lipid A moiety).
LOS is also present on the surface of meningococcal blebs. For many years efforts have been focused on developing meningococcal outer membrane vesicle (or bleb) based vaccines (de Moraes, J. C., Perkins, B., Camargo, M. C. et al. Lancet 340: 1074-1078, 1992; Bjune, G., Hoiby, E. A. Gronnesby, J. K. et al. 338: 1093-1096, 1991). Such vaccines have the advantage of including several integral outer-membrane proteins in a properly folded conformation which can elicit a protective immunological response when administered to a host. In addition, Neisserial strains (including N. meningitidis serogroup B—menB) excrete outer membrane blebs in sufficient quantities to allow their manufacture on an industrial scale. More often, however, blebs are prepared by methods comprising a 0.5% detergent (e.g. deoxycholate) extraction of the bacterial cells (e.g. EP 11243). Although this is desired due to the toxicity of LOS (also called endotoxin) as described above, it also has the effect removing most of the LOS antigen from the vaccine.
A further problem with using LOS as a vaccine antigen is that 12 LPS immunotypes exist with a diverse range of carbohydrate-structures (M. P. Jennings et al, Microbiology 1999, 145, 3013-3021; Mol Microbiol 2002, 43:931-43). Antibodies raised against one immunotype fail to recognise a different immunotype. Although effort has been focused on producing a generic “core” region of the oligosaccharide portions of the LOS immunotypes (e.g. WO 94/08021), the bactericidal activity of antibodies generated against the modified LOS is lost. Thus a vaccine may need to have many LOS components of different immunotype to be effective.
A further problem exists with the use of LOS (also known as LPS or lipopolysaccharide) as antigens in human vaccines, namely that they carry saccharide structures that are similar to human saccharide structures (for instance on human red blood cells), thus posing a safety issue with their use. Yet changing the LOS structure is problematic due to the structural sensitivity of the bactericidal effectiveness of the LOS antigen.
The present invention presents processes for ameliorating one or more of the above problems, and presents methods for making novel vaccines based on meningococcal LOS as a protective antigen, particularly when present on an outer membrane vesicle.